Panel board



i V lms-Lena:- v V Patented July 12, 1932 viwrg w TBS JOHN w. LEDEBOER, ornmnn, PENNSYLVANIA, AssIeNoa "ro nmrnnasnns'ros SHINGLN 8a SHEATEING COMPANY, A CORPORATION OF PENNSYLVANIA x; No Drawing. 1 l iplieaticui filed Ianuarf 22,:1930 Serial This invention relates to boards or slabs of insulating material composed of Portland cement and an inertmaterial impregnated with an insulating compound to give a permalpent dielectric strength to the board or sla. i

The obj ct of the invention is toprovide such a board or slab that will be inexpensive in manufacture and durable in use, and hav- 10 ing a fine smooth surfacefinish.

According to the process of this invention the slab is first formed and hardened and then impregnated with the insulating material. In the formation of the slab Portland cement is mixed with a relatively large amoun of inert material, such as asbestos fibers the asbestosfibers forming) as much obtained as (5% of the total amount of as estos and cement. Preferably the Portland cement is not too quick setting, and the cement and fibers are mixed together with an excess of water and then run into a die having its lower surface of porous material to permit the excess of water to be forced out under pressure about 1500 ounds per square inch. This die-formed s ab in its wet condition is then removed and permitted to set and age or cure for ten days or longer, the edges being sprinkled at intervals with moisture to keep a reasonablyuniform content of mois- ,ture in the slab while it is hardening and 7 avoid irregular effects and warping. This hard cured slab has on one surface the marks of the filter or strainer used in the die to permit the esca e of the excess water, while its opposite surfhce is comparativel smooth due to the contactive action of t e press plate of the die. 7

After the setting and curing the slab is also somewhat irregular in shape and thickness, and the next step in the process is to i grind the surfaces to substantially true parvallelisin with each other and to give very nearly the final thickness ofthe slab. Pref- V erably this grinding is done with the slab in a horizontal position, and with its surface acted upon by a rota grinder carrying segments of the grinding material working 'upon the cement asbestos mixture which is wetted during the grinding. The resulting ground surfaces are porous and of a dull fin ish. While they are substantially plane, the surfaces have a more or less rough ap arance due to the exposed loose ends 0 the contained asbestos fibers at and near the sur- 66 faces, these exposed loose ends appearing at and over substantial portions of the -surfaces. After 'this grinding to accurate fiat form the slab is vacuum-dried at a temperature of about 220 or a on 2 hours, the vacuum '60 being about 28 so'as to remove all excess moisture from the slab. The dried slab is then cooled and sanded in a three-drum sander to givea' finer, smoother surface finish,'but without changing the general characteristics of the surface f i as the'result of the grinding opera- 10D. .4 y a- The dried and sanded slab is then placed in the impregnating tank and redried at a tem erature of 475 F. under 28" vacuum and for a time varying f rom E to l; Hours, depending upon the thickness of the slab. All of the pores and fibers of the slab are thus entirely free ofany excess moisture, and the slab is ready'to' receive the impregnating compound. I In impregnating theredried slab the compound in heated liquid form is run into the v tank so as to submerge the slab, and this compound gradually permeates throughout the entire thickness of the slab, a pressure of eighty ;or ninetypounds per square inch be maintained on the impregnating mate' ma L'i This jg pregating t 11erial is'preferably a mix ure 0 equa par s o as alt and wax tailin The asphalt used 1n impregna ing 1s"fi'o w n as saturating compound and has a melting point of approximately 120 F. and contains about 1% free carbon. The wax- I tailings have a melting point'of 100? F. and contain less than one half of 1% free carbon;

The, time of impregnation varies with the different thicknesses from about 6 hours for thickness to 8-days for a 2" thickness, a

I 1" thicknesstaking about 48 hours and 1% thickness about :96 hours. The admixture'of waxtailings' reduces the viscosity anaemeifs thetinieforimpregnation, 'and'i'n genas insulatingboards andpanel boards for eral increases the efliciency of the operation.

At the end of the period of impregnation the slab is removed from the impregnating tank and cooled and belt-sanded to give it a 5 very smooth surface, the slab itself being substantially black in color. In this condition the slabs are stored in stock and are removed as required from stock and cut to size and machined by boring and the like to final form electrical apparatus. f a.

In order to give a very soft al form" is finish the board or panel in its finely sanded and then puttied so as to cover any slight pits or depressions, and then'lacqueredwith a black lacquer such for instance asfDuco giving a lieaut f ul deep, dull black surfflel'b'iiithe final I 1 T m? T, Y. ,The fiem'ent asbestos material up to ,the time of impregnation is quite porous and is intentionally maintained in this condition for impregnation. A relatively large amount of the material is the inert asbestos fibers,' and careis taken in the pressing of the slab not to overcompact itso as to interfere with the desirable porosity, or compact the material ex-- cessively or render it impervious. Similarly in ;the subsequent grinding and sanding operations theporosity of the surface is 3 maintained so thatit is only the impregnation with the insulating compound that refiders the slab im ervious and vvaterproo f and enables it to be nished smoothly and evenly,

the final lacquering' adding an impervious surface coating over the impregnat1ng'ma terial as a base... The lacquer at the porous surfaces directly. contacts with and forms a bond w1 th hemsulating material, and this gives a very firm bond of the lacquer on 43 the impregnated cement asbestoslmaterial.

Where the slab tends to be slightly brownish; at the edges, this black surface lacquer com-- pletely covers the f brown so that the entire slab is a deep velvety black in appearance, as

i well as smooth, solid and close-grainedvi The process of forming the insulating I boardor panel herein disclosed constitutes I the subject matter of my divisional application Serial No. 613,269 filed May 24,1932.

I claim:

1T1. Insulating panel board and the like comprising a mixture of Portlandcement and asbestos fibers-with the cement set under pressure in porous conditionf'rom a mixture 5 containing-an excess of water, the amount of asbestos being in excess of the amount of said cement before setting and the surfaces of the board being smoothly ground and porous and uncompacted, and 'an impregnating insulating material throughout the board and at the porous ground surfaces thereof to render it solid and close-grained.

2. Insulating panel board and the ;like

comprising a mixture of Portland cement and asbestos fibers with the cement set under;

pressure in porous condition from a mixture containing an excess of water, the amount of asbestos being in excess of the amount of said cement before setting and the surfaces of the board being smoothly ground an porous and uncompacted, and an impregnating insulating material throughout the board and at the porous round surfaces thereof to renderit solid and close-grained, said insulating"material comprising a mixture 0 asphalt and wax taih'ngs.

Insulating panel board and the like comprising a mlxture of Portland cement and asbestos fibers with the cement setunder "pressure in porous c'ondltlon from a mlxture containing an excess of water, the amount of asbestos being in excess of the amount of said cement before setting and the surfaces of the board being smoothly ground and porous and uncompacted,'.an impregnating insulating material throughout the board and 'at the porous ground surfaces thereof to render it solid and [close-grained, and a lacquer layer at the porous surfaces forming a bond with said insulating material:

JOHN. W.- LE EBOERJ 

